Conventional inorganic electronic devices such as cathode ray tubes are bulky and inefficient compared to alternative organic electronic devices. Organic electronic devices that emit light, such as organic light-emitting diodes (OLEDs) are potentially useful for flat panel displays. In all such organic electronic devices, an organic active layer having an organic electroluminescent compound is sandwiched between two electrical contact layers. At least one of the electrical contact layers is light-transmitting (transparent) at some wavelengths so that light can pass through the electrical contact layer and escape the device. The organic active layer emits light through the light-transmitting electrical contact layer when a voltage is applied across the electrical contact layers.
One type of organic electroluminescent device is an organic light-emitting diode (“OLED”). Some organic electroluminescent compounds that make up the active component in OLEDs include small molecules, such as organometallic complexes and dyes, and large molecules such as conjugated polymers.
OLED devices frequently include one or more charge transport and/or anti-quenching layers, which are typically positioned between the light-emitting layer and one of the contact layers. A charge transport layer may be a hole transport layer or an electron transport layer or both. A hole transport layer may be positioned between the light-emitting layer and the anode contact layer which provides holes into the light-emitting layer. An electron transport layer may be positioned between the light-emitting layer and the cathode contact layer, which injects electrons into the light-emitting layer.
Charge transport materials are also useful in transport layers acting as photoconductors used in imaging products such as xerography and laser printers. (R. B. Seymour, ed., “Conductive Polymers”, Plenum Press, New York, 1981); as molecular transistors (C. R. Kagan, and P. Andry, “Thin Film Transistors, Marcel Dekker, New York, 2003) and as elements in organic photovoltaics (P. Peumans, A. Yakimov, and S. R. Forrest, J. Apply. Phys., 93, 3693 (2003)).
There remains a need for new charge transport materials.